Retention of Structural Cores in the Synthesis of High-Nuclearity Polyoxoalkoxomolybdate Clusters Encapsulating [Na(H2O)3]+ and [MoO3] Moieties

M. Ishaque Khan, Qin Chen, Jose Salta, Charles J. O'Connor, Jon Zubieta

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Abstract

Hydrothermal reactions of molybdenum-oxide precursors with polyalcohols in the presence of base yielded two series of mixed-valence oxomolybdenum clusters, the hexadecanuclear species [XH12(MoVIO3)4Mov 12O40]m- (X = Na+, m = 7; X = 2H+, m = 6) and the superclusters [XHnMoVI6MoV36O 109{(OCH2)3CR}7]m- (X = Na-(H2O)3+, m = 9, n = 13; X = Na(H2O)3+, m = 7, n = 15; X = MoO3, m = 9, n = 14; X = MoO3, m = 10, n = 13). In a representative synthesis for the hexadecanuclear class of materials, the hydrothermal reaction of a mixture of Na2MoO4·2H2O, MoO3, Mo metal, and NH4Cl produced (NH4)7[NaMo16(OH)12O 40]·4H2O (1·4H2O) as red-orange crystals. The compound (Me3NH)4K2[H2Mo 16(OH)12O40]·8H2O (2·8H2O) was prepared in a similar fashion. The structure of the anion of 1 consists of an ε-Keggin core {H12Mo12O40}, capped on four hexagonal faces by {MoO3} units and encapsulating a Na+ cation. The structure of the oxomolybdenum framework of 2 is essentially identical to that of 1; however, the central cavity is now occupied by 2H+. The synthesis of the "superclusters" exploits similar hydrothermal conditions, resulting in the isolation of (Me3NH)2(Et4N)Na4[Na(H 2O)3H15-Mo42O 109{(OCH2)3CCH2OH} 7]· 15H2O (3· 15H2O), (Me3NH)2(H3O)Na6[Na(H 2O)3H13Mo42O109{(OCH 2)3CCH2- OH}7]·7H2O (4·7H2O), Na9[(MoO3)H14Mo42O 109{(OCH2)3CCH2OH} 7]·0.5C(CH2OH)4· 25H2O (5·0.5C(CH2-OH)4-25H2O), and (Me4N)(Et2NH2)(H3O) 2Na6 [(MoO3)H13Mo42O109{(OCH 2)3CCH3}7]·10H2O (6·10H2O). The structures of these superclusters resemble a bowl consisting of an oxomolybdenum framework, constructed from eighteen pairs Mo(V) - Mo(V) dimers and linked through edge-sharing of {MoO6} octahedra, with six cis-dioxomolybdate(VI) sites protruding outward to provide the surface of a channel to the molecular cavity of the complex anion. The cavity is populated by a Na(H2O)3+ group in 3 and 4 and by a {MoO3} unit in 5 and 6. Crystal data are as follows. 1·4H2O: cubic F4̄3m (No. 216), a = 26.978(3) Å, Z = 8. 2·8H2O: orthorhombic Cmcm (No. 63), a = 18.493(4) Å, b = 19.685(4) Å, c = 19.518(4) Å, Z= 4. 3·15H2O: triclinic P1̄ (No. 2), a = 22.159(4) Å, b = 27.049(5) Å, c = 17.726(3) Å, a = 98.34(1)°, β= 112.56(2)°, γ = 82.81(1)°, Z = 2. 4·7H2O: monoclinic C2/c (No. 15), a =_54.901(11) Å, b = 17.616(4) Å, c = 36.571(7) Å, β= 94.04(2)°, Z = 8. 5·0.5C(CH2OH)4·25H2O: triclinic P1̄ (No. 2), a = 17.302(3) Å, b = 20.865(4) Å, c = 26.734(5) Å, α = 103.90(3)°, β= 99.26(3)°, γ = 108.95(3)°, Z = 2. 6·10H2O: orthorhombic Pbcm (No. 57), a = 17.916(4) Å, b = 44.614(9) Å, c = 23.472(5) Å, Z = 4.

Original languageEnglish (US)
Pages (from-to)1880-1901
Number of pages22
JournalInorganic Chemistry
Volume35
Issue number7
StatePublished - Dec 1 1996

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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